Retrieval device

ABSTRACT

An endoscopic surgical device for retrieving severed tissue or foreign bodies from within a subject is disclosed. The device comprises a support unit and a tissue retrieving net system. The net system is carried by the support unit and may be inserted into the subject through an orifice or small incision and operated to retrieve tissue that has been severed by a conventional method. The net system comprises a net, a net actuator, a net deployment and retrieval assembly for transmitting motion between the net and its actuator. The net system further comprises at least one net connector disposed such that only one connector is within an articulation zone, defined by locations of severe bending of the device during operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This non-provisional application claims benefit of U.S. PatentProvisional Application Serial No. 60/292,168, entitled “RetrievalDevice,” filed on May 18, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates to surgical devices and moreparticularly to endoscopic retrieval devices constructed for retrievingrelatively small pieces of sample tissue or foreign bodies from a humansubject through orifices or small incisions.

BACKGROUND OF THE INVENTION

[0003] Snares, baskets, and graspers are in widespread use for severingcapturing and retrieving tissue specimens and foreign bodies from withinsubjects. The devices are used in human and animal subjects, inlaparoscopic surgeries and other procedures where access within asubject is only possible via a small opening. One exemplary use is forcutting off and retrieving intestinal polyps where a wire snare, passedthrough an colonoscope instrument channel, encircles and is tightenedabout an intestinal polyp to sever the polyp. The severed polyp isretrieved in a net inserted through the instrument channel. The net ismanipulated to enclose the polyp and then withdrawn with the instrumentso that the tissue architecture remains undisturbed.

[0004] In this procedure, as well as others, the net and snare must bequite compact in order to pass into the subject through the instrumentchannel, or other passage. Prior art proposals have employed snaressupported within plastic tubes that were snaked into the subject tolocate the snare where desired. The snare was then deployed from itstube, manipulated to cut off the polyp and retrieved into the tube forremoval from the subject.

[0005] A net, collapsed within another tube, was introduced through theinstrument channel, etc., for removing the polyp. When near a targetpolyp, the net was deployed, like the snare, and manipulated to net thepolyp. The net was then closed sufficiently to secure the polyp andwithdrawn from the subject.

[0006] U.S. Pat. No. 5,643,283 to Younker, which is incorporated hereinby reference in its entirety, discloses a device for retrieving anobject from within a subject. The device comprises a shaft and acompressible pouch for receiving the object positioned adjacent a distalend of the shaft. The pouch includes a mouth which can be opened andclosed. The pouch is retained, in proximity to the distal end of theshaft, on a cable loop by a slidable tether. The net is free to slide onthe cable loop to form a pouch at the distal end of the shaft. Thetether is fixed at a second location near the proximal end of the shaft,and in one embodiment, is tied off to a ring and secured with heatshrink tubing. When the targeted foreign object is within the pouch, aclinician disengages the ring portion of the handle to close the netaround the object. The clinician then removes the device from thepatient and unloads the object from the net. The clinician then placesthe ring on a post, in order to pack the pouch into the distal end ofthe shaft.

[0007] In operation of a commercial embodiment of U.S. Pat. No.5,643,283, several problematic issues have surfaced. Clinicians haveexperienced difficulty in understanding the operation of the tether, inparticular, the interaction of the ring and post. The ring is to be usedto pull the net inside the shaft only when an object is not within thenet. In preparation to capture an object, the ring should be disengagedto release the net. The net is then slid over the targeted object andthe net is closed. At this point, proper operation would involve merelyremoving the device from the patient. However, some clinicians whenoperating the device try to further pull the net inside the shaft whenthe net is bundled up at distal end of cable loop. This will cause thenet to jam, or in some cases, damages the tubing. The occasionalimproper operation of the device sometimes causes permanent malfunction.

[0008] The commercial embodiment discussed above also adds undesirableexpense to the product. Specifically, the full length tether and heatshrink operation add material cost and labor assembly cost to thedevice.

[0009] The present invention provides a new and improved retrievaldevice that is so constructed and arranged that net movement duringdeployment and retrieval is not prohibitively restricted. Secure netattachment is assured and that provides for convenient net packing inthe introducer passage. The device provides a convenient and economicalmethod of sample retrieval during endoscopic procedures. The newretrieval device is easy assemble, manufactured at a reduced cost, andeasier to use by the end consumer.

SUMMARY OF THE INVENTION

[0010] In one illustrated embodiment of the present invention anendoscopic surgical device for retrieving severed tissue from within ahuman subject is provided. The device includes a support unit and atissue retrieving net system.

[0011] The support unit includes a body and an elongated introducermember. The body defines a first passage therethrough. The introducerhas a first end section proximal and fixed with respect to the body anda second end section remote from the body. The introducer member furtherdefines a second passage aligned with the first passage and opening atthe second end section.

[0012] The tissue retrieving net system includes a net, a net deploymentand retrieval assembly and a net actuator system.

[0013] The net includes a wire-like resilient loop and a net elementhaving a mouth section slidably disposed on the loop and a tissuereceiving pouch section. The loop terminates with two relativelyparallel loop cables. The net is disposed adjacent the second end fordeployment and retraction through the second passage opening.

[0014] The net deployment and retrieval assembly extends substantiallythrough the first and second passages and connects to the net. Theassembly further includes a motion transmitting member extending in thesecond passage to the loop.

[0015] The net actuator unit includes a first handle fixed with respectto the body and a second handle fixed with respect to the motiontransmitting member and movable relative to the first handle. The act ofshifting the second handle relative to the first handle shifts the netinto and out of the second passage opening.

[0016] The introducer member second passage has a diameter substantiallysmaller than the width of the loop as deployed. The member engages theloop at the second end section opening and resiliently collapses andelongates the loop as the net is retracted and moves into the introducermember passage. The loop resiliently returns to its uncollapsedconfiguration as it is deployed.

[0017] In one embodiment, the net system includes at least one connectoradapted to fasten each loop cable. The ends of the net element aresecured to the motion transmitting member on the proximal side of the atleast one connector with respect to the support unit.

[0018] In a second embodiment, the net system further includes a firstconnector, a second net connector proximal to the second passageopening, and an intermediate portion defined by an axial space on theloop cables between the first connector and the second connector. Thefirst connector and the second connector are adapted to fasten each loopcable. Ends of the net element are secured to the loop within theintermediate loop portion between the first connector and the secondconnector.

[0019] The deployment and retrieval assembly may include a thin,flexible wire-like motion transmitting member between the net actuatorunit and the loop. The motion transmitting member extends within anintroducer guide passage which closely surrounds the motion transmittingmember and constrains the member for translational longitudinal motionwithin the passage.

[0020] The first connector may be disposed at least 6 inches from thesecond connector, such that only one connector is within an articulationzone during deployment of the net element.

[0021] The ends of the net element may be secured to the motiontransmitting member adjacent a proximal shoulder of the connector withrespect to the support unit.

[0022] The present invention offers advantages over devices available inthe prior art. In a second embodiment, the net is fixed distally andproximally by the use of a first and second connector. The connectorsare sufficiently spaced apart to provide secure net attachment withoutthe use of additional tether mechanisms. The connectors are positionedsuch that only one may be within an articulation zone of the endoscopeat a time, permitting ease of net deployment in a variety of geometricoperating configurations.

[0023] In a first embodiment, only one connector is used to secure theproximal side of the net. This technique decreases the amount of cableloop length within the articulation zone. The reduction in cable looplength effectively reduces the amount of rigid material within thearticulation zone of the endoscope at a time, further permitting ease ofnet deployment in a variety of geometric operating configurations.

[0024] The device is also easier to assemble and less expensive tomanufacture than certain conventional designs.

[0025] Further features and advantages of the invention will becomeapparent from the following detailed description made with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is an elevational view of a surgical device constructedaccording to one embodiment of the present invention, illustrated withthe net element deployed;

[0027]FIG. 2 is a view similar to FIG. 1, illustrated with the netelement retracted;

[0028]FIG. 3 is an enlarged fragmentary view of a part of the deviceillustrated in FIG. 1, showing detail of the introducer member;

[0029]FIG. 4 is a enlarged fragmentary view of part of the deviceillustrated in FIG. 1, with the device show as positioned in a sampleconfiguration within a subject;

[0030]FIG. 5 is an enlarged fragmentary view of part of a surgicaldevice constructed according to a second embodiment of the presentinvention, showing detail of the introducer member; and

[0031]FIG. 6 is a enlarged fragmentary view of part of the deviceillustrated in FIG. 5, with the device show as positioned in a sampleconfiguration within a subject.

BEST MODE CONTEMPLATED FOR CARRYING OUT THE INVENTION

[0032] An endoscopic surgical device 10 for retrieving severed tissueand or foreign bodies from within a subject is illustrated by thedrawings. Referring to FIGS. 1 and 2, in one embodiment, the device 10comprises a support unit 12 and a tissue retrieving net system 16. Thenet system is carried by the unit 12 and is so constructed and arrangedthat it may be inserted into the subject through an orifice or smallincision and operated to retrieve a tissue sample previously detachedfrom the subject by a conventional method, e.g., a snare/cautery system.Accordingly, the net system 16 comprises a net 20, a net actuator 24,and a net deployment and retrieval assembly 28 for transmitting motionbetween the net and its actuator 24. The net 20 comprises a net element21 and a net loop 22 and a distal 25 and proximal 26 tie off suture thatsecures the net.

[0033] The device 10 can be used with any suitable or conventionalendoscopic or laparascopic surgical equipment. For purposes of thisdisclosure the device 10 is described in the context of use with anendoscope/colonoscope/sigmoidoscope type apparatus (not illustrated), ofconventional or suitable construction. The scope is provided with anelongated body having a controllably flexible projecting end re-ion.Surgical instruments, such as the device 10, may be introduced throughan instrument channel, which extends through the scope body, forretrieving tissue targeted by the surgeon manipulating the scope.

[0034] The support unit 12 supports the net system 16 so that the net 20can be inserted through the scope instrument channel by a surgeon. Thesupport unit 12 comprises a body 30 defining a passage and an elongatedintroducer 40 having a first end section 42 proximal and fixed withrespect to the body 20 and a second end section 44 remote from the body.The introducer 40 is tubular and aligned with the body passage forreceiving the net system.

[0035] The illustrated introducer 40 is a smooth, supple member capableof being snaked through the scope instrument channel into the subjectand readily flexed into any shape required as the scope body is flexedby the surgeon. In the illustrated embodiment, the introducer 40 is agenerally cylindrical, small diameter tube formed of non-reactive lowfriction plastic material, such as polytetrafluouroethylene. The firstend section 42 is fixed to the body 30 while the second end section 44houses the net for individual deployment and retrieval.

[0036] The net actuator 24 is adapted for reciprocating the deploymentand retrieval assembly in the body and introducer to operate the net 20.The actuator 24 comprises a first handle 50 fixed with respect to thebody 30 and a second handle 52 attached to the deployment and retrievalassembly 28 and movable with respect to the handle 50.

[0037] The second handle 52 is fixed to the assembly 28 and mounted onthe handle 50 between its ends for longitudinal sliding movement. Thesecond handle comprises a dual finger ring member 80 slidable on thehandle 50. The handles 50, 52 as illustrated are formed from moldedplastic materials.

[0038] The deployment and retrieval assembly 28 is constructed andarranged to transmit considerable deployment and retractive forces tothe net while enabling the scope body to be freely manipulated andflexed to position the net where desired. The assembly 28 comprises alink comprises a first link section 70 and a second link section 71connected to the actuator 24 for transmitting compressive and tensileforces between the handle 52 and a bore 58. The bore 58 is disposedwithin the center of the body 30. The link 70 transmits relativelysubstantial compressive forces without bending or breaking. Theillustrated first link section 70 is formed from hypodermic needlestock, i.e., it is a cylindrical stainless steel tube. The second linksection 71 as illustrated is a multi-strand cable. The first linksection 70 joins the second link section 71 as the link exits the body30.

[0039] The link 71 extends from the body 30 and within the introducer 40so that it must flex with the introducer yet transmit compressive andtensile forces. The illustrated link 71 is closely surrounded by thebody passage of the introducer passage 40. The link 71 is relativelystiff compared to the supple introducer. When transmitting compressiveforces, the link 71 is resiliently deformed to bow against theintroducer wall. The link 71 has good compressive and tensile strengthand is somewhat resiliently bendable. The link 71 will bend appreciablywithout yielding and kinking.

[0040] A first connector 80 and a second connector 82 fix the loop 22 intwo locations with respect to the net 20. The proximal side of the netis tied off at a location 85 between the loop cables. As illustrated inFIG. 3, a tether 27 is used to tie off the proximal side of the net.

[0041] This tether is shorter than conventional tethers that travel thefull length of the introducer. No further tethering system is required,although additional net mounting techniques may be employed in thepractice of the invention.

[0042] Referring now to FIG. 3, the first connector 80 joins the link 71and the loop 22 together structurally. The illustrated connector 80 is ashort tube crimped to both ends of the loop 22 and to the second linksection 71. The illustrated connector tube is crimped about the loop andlink to form a cross sectional shape, which is capable of rotatingwithin the introducer 40. The illustrated connector 80 is formed fromhypodermic needle stock, like the first link section 70. The secondconnector 82 further joins opposing portions on the net loop 22 at alocation proximal to the net 20 with respect to the first connector 80.

[0043] In the illustrated embodiment, the space between the two loopcables is utilized to fix the net element 21 with respect to the link71. An intermediate region R, shown in FIG. 3, axially between the firstconnector 80 and the second connector 82 within the introducer 40 may beused. In an exemplary embodiment, the proximal side of the net element21 with respect to the support system 12 is fixed to the net loops 22 ata convenient location 85. Suture material, or another known suitablemethod, may be used to tie the net to the loop.

[0044] The net 20 is deployed from the introducer second end 44 andmanipulated by the surgeon to net severed tissue and secure the tissuefor retrieval from the subject. The net 20 may be deployed after a snareor similar technique has severed the target tissue. The net 20 comprisesa pouch-like net element 21 slidably supported on the loop 22.

[0045] The illustrated net loop 22 is formed from a loop of fine wireconstructed and arranged to cooperate with the introducer to deploy andretract the net 20. The illustrated loop 22 is a stiff, resilientflexible wire having its respective ends crimped in place in twolocations by the first and second connector 80, 82. When the net isdeployed from the end of the introducer, the loop resiliently expands toa relaxed condition where the loop width is substantially greater thanthe introducer diameter. The deployed snare is guided to a positionwhere it receives a target polyp or other tissue. The net is retractedby the surgeon. As the net is retracted into the introducer second end44 the loop resiliently bears against the introducer wall so the loopresiliently collapses, narrowing the loop portion projecting from theintroducer. Tissue or another object captured within the net element 21is progressively constricted by the elastic nature of the net, allowingfor a wide range of sized objects to fit inside the net withoutcompromising the architecture preservation or the security of theobject, as the net is being drawn toward the distal end of theintroducer.

[0046] The net element 21 is an extremely light pouch-like structurehaving the net loop wire extending through the mesh about its peripheryto form a net mouth slidably supported on the loop and a dependingpouch. The net fibers are quite fine, yet sufficiently strong that thenet element may slide along the loop wire in the direction away from theconnectors 80, 82 to enclose tissue within the pouch as the net isretrieved and/or to gather the entire net at the distal net loop endwhen the net loop has been retrieved. The net has minimal bulk so thatwhen an empty net is retrieved, it easily moves completely into theintroducer passage.

[0047] The illustrated net is formed from 100% nylon fibers havingstrand diameters of from about 0.0125 mm-0.04 mm. The fibers are wovenin a diamond mesh pattern with the mesh strands spaced from 1 mm-3 mmand their intersections fixedly secured together. The illustratednetting material is substantially like that of a fine mesh hair net. Thenet is formed by cutting about a square, circular or elliptical sectionof the net, trimming or otherwise finishing the edges and threading theloop wire through the peripheral mesh elements. The cut net section sizeis selected sufficiently larger than the net loop area to assure that apouch-like, tissue receiving portion suspends from the net mouth, butnot too large to create undesirable bulk and difficulty packing the netwhen pulling it inside the shaft.

[0048] Attempting to fully retrieve a tissue containing net into theintroducer 40 can result in tissue loss by forcing the tissue throughthe net. The net fibers are fine and strong so they may cut the tissueor they may be broken, either of which alternative is undesirable. A netactuator thumb ring may be provided with a tag (not illustrated) warningthe surgeon not to continue retrieving the net against unusualresistance.

[0049] The present invention resolves problems faced by surgeons andnurses working with some prior art designs. Nurses and doctors haveexperienced difficulty in understanding the operation of the tether,specifically the interaction of the ring and post. Therefore,occasionally the device is operated incorrectly causing malfunction. Thepresent design allows a nurse to pull back on the handle to convenientlypack the net inside the introducer passage.

[0050] Further, often a surgeon is required to manipulate the endoscopeinto difficult to access internal areas. Certain procedures requirebending or twisting the endoscope. The area of the endoscope that istwisted or bent is called the articulation zone.

[0051] Some net devices have featured multiple connector designs inwhich the connectors are spaced somewhat adjacently with the second endsection 44. In these designs, the multiple connectors on the net deviceshave resisted bending of the scope. Moreover, the friction created hasmade deployment of the net difficult once the scope has been desirablypositioned by the surgeon. One advantage of the present invention isincreased freedom of movement, and ease of net deployment, within thearticulation zone.

[0052] During operation of the system 10, the surgeon experiences anincreased ease of use over prior art designs. In the illustratedembodiment, the first connector 80 is axially disposed a distance fromthe second connector 82, such that only one connector is within thearticulation zone (bounded by A₁,A₂), defined along the introducer 40longitudinal axis, during deployment of the net element. In theillustrated system, the first connector 80 is disposed at least sixinches from the second connector 82.

[0053] The articulation zone defines the axial portion of the introducer40 within a substantially non-linear position. The articulation zonetypically includes bends of greater than 30° and can exceed 200° at aradius of 0.75 inches or less.

[0054] Referring to FIG. 4, a portion of the system 10 is illustrated aspositioned in a probable configuration within a subject. Duringoperation of the scope, a surgeon may manipulate the second end section44 of the introducer into a severe articulated position. At times, thesecond end section may be bent up to 180°, as illustrated in FIG. 4.Deployment of the net 20 in this and similar positions is difficult whenthe connectors 80, 82 are both within the articulation zone. Thecombined kinetic frictional force of each connector against the insideof the introducer passage would otherwise make deployment of the netdifficult. As illustrated in FIG. 4, the surgeon more easily deploys thenet in a variety of positions.

[0055] A second embodiment of the present invention is illustrated bythe drawings. A part of an endoscopic surgical device 10 for retrievingsevered tissue and or foreign bodies from within a subject isillustrated in FIGS. 5 and 6. In this illustrated design, the device 10includes a support unit 12 and net actuator 24 as previously described.However, an alternative construction of a net deployment and retrievalassembly 28 is utilized.

[0056] In the illustrated design, the net deployment and retrievalassembly 28 uses a single connector. Referring now to FIG. 5, theconnector 182 joins the link 71 and the loop 22 together structurally.The illustrated connector 182 is a short tube crimped to both ends ofthe loop 22 and to the second link section 71. The illustrated connectortube is crimped about the loop and link to form a cross sectional shape,which is capable of rotating within the introducer 40. The illustratedconnector 182 is formed from hypodermic needle stock, like the firstlink section 70.

[0057] One goal of the design is to reduce the amount of rigid materialwithin the articulation zone. During operation of the system 10, thesurgeon experiences an increased ease of use over prior art designs. Asillustrated in FIG. 6, the length of rigid material within thearticulation zone (bounded by A₁,A₂), defined along the introducer 40longitudinal axis, is minimized during operation of the net element. Thereduction in rigid material results from reducing the length of loopcable 22 within the articulation zone.

[0058] As shown in FIG. 5, the proximal side of the net element 21 withrespect to the support system 12 is fixed to the net loops 22 at aconvenient location 185. Suture material, or another known suitablemethod, may be used to tie the net to the loop. As illustrated in FIG.5, a tether 27 is used to tie off the proximal side of the net. Thistether is shorter than conventional tethers that travel the full lengthof the introducer. The tether 27 may be tied off adjacent the shoulderof the connector 182. As shown, the tether has a diameter not greaterthan the thickness of the connector shoulder. No further tetheringsystem is required, although additional net mounting techniques may beemployed in the practice of the invention.

[0059] While two embodiments of the invention has been illustrated anddescribed in considerable detail, the present invention is not to beconsidered limited to the precise constructions disclosed. Variousadaptations, modifications and uses of the invention may occur to thoseskilled in the arts to which the invention relates. It is the intentionto cover all such adaptations, modifications and uses falling within thescope or spirit of the annexed claims.

Having described my invention I claim:
 1. An endoscopic surgical devicefor retrieving severed tissue or foreign bodies from within a humanbody, the device comprising: a. a support unit comprising: i. a bodydefining a first passage therethrough; and ii. an elongated introducermember having a first end section proximal and fixed with respect tosaid body and a second end section remote from the body, the introducermember defining a second passage aligned with the first passage andopening at said second end section; and b. a tissue retrieving netsystem comprising: i. a net comprising a wire-like resilient loop and anet element having a mouth section slidably disposed on the loop and atissue receiving pouch section, said loop terminating with tworelatively parallel loop cables, said net disposed adjacent said secondend for deployment and retraction through said second passage opening;ii. a net deployment and retrieval assembly extending substantiallythrough said first and second passages and connected to the net, saidassembly comprising a motion transmitting member extending in saidsecond passage to said loop; and, iii. a net actuator unit comprising afirst handle fixed with respect to said body and a second handle fixedwith respect to said motion transmitting member and movable relative tosaid first handle so that shifting the second handle relative to saidfirst handle shifts said net into and out of said second passageopening; c. said introducer member second passage having a diametricalextent substantially smaller than the width of said loop as deployed,said member engaging said loop at said second end section opening andresiliently collapsing and elongating said loop as said net is retractedand moves into said introducer member passage, said loop resilientlyreturning to its uncollapsed configuration as it is deployed; d. saidnet system further comprising a first connector, a second net connectorproximal to second passage opening, and an intermediate portion definedby an axial space on the loop cables between the first connector and thesecond connector, wherein the first connector and the second connectorare adapted to fasten each loop cable, and ends of said net element aresecured to the loop within the intermediate loop portion between thefirst connector and the second connector.
 2. The device claimed in claim1 wherein said deployment and retrieval assembly comprises a thin,flexible wire-like motion transmitting member between the net actuatorunit and the loop, said motion transmitting member extending within anintroducer guide passage, said introducer guide passage closelysurrounding said motion transmitting member and constraining said memberfor translational longitudinal motion within said passage.
 3. The deviceclaimed in claim 1 wherein said first connector is disposed at least 6inches from said second connector, such that only one connector iswithin an articulation zone during deployment of the net element.
 4. Anendoscopic surgical device for retrieving severed tissue or foreignbodies from within a human body, the device comprising: a. a supportunit comprising: i. a body defining a first passage therethrough; andii. an elongated introducer member having a first end section proximaland fixed with respect to said body and a second end section remote fromthe body, the introducer member defining a second passage aligned withthe first passage and opening at said second end section; and b. atissue retrieving net system comprising: i. a net comprising a wire-likeresilient loop and a net element having a mouth section slidablydisposed on the loop and a tissue receiving pouch section, said loopterminating with two relatively parallel loop cables, said net disposedadjacent said second end for deployment and retraction through saidsecond passage opening; ii. a net deployment and retrieval assemblyextending substantially through said first and second passages andconnected to the net, said assembly comprising a motion transmittingmember extending in said second passage to said loop; and, iii. a netactuator unit comprising a first handle fixed with respect to said bodyand a second handle fixed with respect to said motion transmittingmember and movable relative to said first handle so that shifting thesecond handle relative to said first handle shifts said net into and outof said second passage opening; c. said introducer member second passagehaving a diametrical extent substantially smaller than the width of saidloop as deployed, said member engaging said loop at said second endsection opening and resiliently collapsing and elongating said loop assaid net is retracted and moves into said introducer member passage,said loop resiliently returning to its uncollapsed configuration as itis deployed; d. said net system further comprising a connector, whereinthe connector is adapted to fasten each loop cable, and ends of said netelement are secured to the motion transmitting member on the proximalside of the connector with respect to said support unit.
 5. The deviceclaimed in claim 4 wherein said deployment and retrieval assemblycomprises a thin, flexible wire-like motion transmitting member betweenthe net actuator unit and the loop, said motion transmitting memberextending within an introducer guide passage, said introducer guidepassage closely surrounding said motion transmitting member andconstraining said member for translational longitudinal motion withinsaid passage.
 6. The device claimed in claim 4 wherein the ends of saidnet element are secured to the motion transmitting member adjacent aproximal shoulder of said connector with respect to said support unit.